The present invention relates to a method of forming and processing an advancing endless synthetic filament yarn, and specifically to a method of withdrawing the yarn from a spinneret or a drawing zone by means of a feed system, and then winding the yarn onto a rotating tube to form a yarn package. A method of this type is described, for example, in the trade journal "Chemiefasern/Textilindustrie", September 1991, pp. 1002, 1004. See also DE-A 22 04 397.
The known method is a single-step spinning method for the production of a multifilament yarn, in which the yarn is withdrawn from the spinneret at a high speed by the feed system, and subsequently wound by means of a takeup system. The feed system comprises two godets which are each looped by the yarn at 180.degree.. This means that the yarn tension above the godets starts with a lower withdrawal tension and increases continuously toward the draw rolls by reason of air friction and other frictional influences until reaching the tension under which the yarn contacts the draw rolls. In this process, the yarn tension is increased such that the freshly spun yarn undergoes a complete or partial drawing. It is, however, undesirable and unsuitable to wind the yarn on the package at the same high tension as well. According to the described method, the two godets have a polished surface which has been hard chrome plated. This generates high frictional resistance between the yarn and the draw roll surface, in respect of both sliding friction and static friction. To achieve the necessary decrease in yarn tension, it is necessary that the spin-takeup apparatus have two godets or godets with a yarn displacement roll so as to achieve an adequate reduction of yarn tension and a good uniformity (Uster value). At delivery speeds in excess of 5000 m/min., in the production of yarns consisting of very thin filaments the known method suffers from the disadvantage that filaments often break, and that the broken filaments can no longer be advanced by the godet, but are entrained by air currents which surround the godet, and are subsequently formed into a lap on the godet. Such a lap results in an interruption of the operation. Likewise, the threading of the yarn is rendered difficult, since the yarn breaks due to the great difference in speed. It is also very difficult to adjust the speeds of the feed system on the one hand and of the takeup system and yarn traverse motion on the other. It is necessary that these speeds are adjustable independently of one another. However, their adjustment relative to each other must be very accurate to prevent tearing or slackening (too low yarn tension). Here, too, there exists a potential for damaging the yarn or interrupting the operation by breaking or forming laps. In particular, it is necessary that the circumferential speed of the yarn takeup package be somewhat lower than the circumferential speed of the feed system. On the other hand, it should not be substantially lower than the geometric sum of circumferential speed of the yarn package and the traverse speed, at which the yarn reciprocates along the package. Finally, in this process it is difficult to set the desired yarn tension at a constant level.
The disadvantages of the above process are avoided by in the so-called godet-free spinning. In this process, the yarn is directly withdrawn from the spinneret directly by the yarn takeup package. However, this results in the disadvantage that between the spinneret and the takeup the yarn is subjected to the tension required for fully or partially drawing the yarn. The tension under which the yarn is wound is thus still higher than the tension necessary for the drawing operation. Consequently, a godet-free spinning is possible only with such takeup systems which have an integrated godet for decreasing tension. In this respect, reference may be made to the takeup system disclosed in DE-C 23 45 898 and U.S. Pat. No. 3,861,607. In these takeup machines, the yarn loops about a grooved roll, which is part of the yarn traversing system, at an angle of 60.degree. to 120.degree. before advancing onto the package. This grooved roll may be operated at a circumferential speed which is greater than the circumferential speed of the package, thereby making it possible to decrease the yarn tension and to spin without godets. As a result, such yarn winding machines have become successful in the godet-free spinning process.
In the yarn winding apparatus as disclosed in German Patent DE 30 16 662, the same effect may be achieved in that the yarn advances first via a yarn traversing system, and over a smooth roll which may rotate at a higher circumferential speed than the takeup package, and finally via a second yarn traversing system to the package. Since this system uses a smooth roll, and since the yarn is looped by 180.degree., there is a risk of laps being formed, and other problems arising from the threading of the yarn. This applies in particular to the adjustment of the roll relative to the speed adjustment of package and yarn traversing system.
A common aspect of the known processes is that they are based on the attempt to obtain in one operating step fully or partially oriented yarns (FOY or POY), while avoiding a buildup of high yarn tensions on the package. Although a godet would be suitable for such a purpose, it entails problems of the kind noted above.
It is accordingly an object of the present invention to provide a yarn processing method of the described type, and which achieves the desired decrease of the yarn tension before the yarn enters into the takeup system, while simultaneously avoiding the disadvantages of the known godets.